A variety of hemorrhagic disorders are caused by the lack of blood coagulation factors. The most common disorders are hemophilia A and B caused by deficiencies or abnormality of blood coagulation factors VIII and IX, respectively.
Hemophilia A is a genetic bleeding disorder caused by an X-linked recessive trait of defective factor VIII gene. A concentrate of a plasma-derived or recombinant factor VIII has been used for the treatment of hemophilia A. Hemophilia B is caused by a deficiency or dysfunction of factor IX, which is treated by using a concentrate of plasma-derived or recombinant factor IX. However, the emergence of alloantibodies against the replacement factors remains as a serious medical problem in the treatment of hemophilia A and B. Antibodies against factor VIII are generated in up to 30% of patients with hemophilia A. Although antibodies against factor IX are less produced, they are less sensitive to an immune tolerance induction therapy, leading to more serious results.
Blood coagulation is initiated by the formation of a complex between tissue factor exposed to circulating blood after a vessel wall damage and an activated form of factor VII (FVIIa). Such complex activates factor IX and factor X and the resultant factor Xa produces the limited amount of thrombin. In a positive feedback loop, thrombin activates a variety of factors (such as factor VIII, factor V, factor XI, etc.) of blood coagulation cascade, and the activated factors constitute a factor Xase complex or a prothrombinase complex. These complexes further amplify their own generation and the production of thrombin. This sufficient amount of thrombin called ‘thrombin burst’ converts fibrinogen at bleeding sites to fibrin, thereby achieving complete hemostasis. However, in case of hemophilia patients having a high concentration of neutralizing antibodies against factor VIII or factor IX, no sufficient hemostasis is attained since the factor Xase complexes mentioned above can't be produced. FVIIa has been used as a major therapeutics for the patients who have neutralizing antibodies against factor VIII or factor IX, because it can activate factor X, even in the absence of factor VIII and factor IX, thereby ultimately producing a sufficient amount of thrombin to achieve the desired therapeutic effects.
FVII is a single-chain glycoprotein consisting of 406 amino acids, has a molecular weight of 50 kDa, and is secreted into blood stream as a zymogen. FVII consists of four distinct domains, i.e., an amino terminal-carboxyglutamic acid (Gla) domain, two epidermal growth factor (EGF)-like domains and a serine protease domain (Hagen F S et al., Proc. Natl. Acad. Sci. USA, 83(8):2412-2416, 1986). FVII is converted to its activated form, FVIIa, by forming two polypeptide chains linked by a disulfide bond, i.e., N-terminal light chain (24 kDa) and C-terminal heavy chain (28 kDa) through the proteolysis of a single peptide bond located at Arg152-Ile153. FVII is present at a concentration of 500 ng/mL in plasma, and 1% (i.e., 5 ng/mL) of FVII is present as FVIIa.
Meanwhile, it has been reported that the half-life of FVII in plasma is approximately 4 hours (3˜6 hours), while that of FVIIa is about 2.5 hours. Due to the short half-life, FVIIa is required to be administered via multiple intravenous injections or continuous injection. However, this would limit the therapeutic uses of FVIIa in terms of high treatment expenses and making the patient's discomfort.
To overcome these problems, methods have been provided for preparing fusion proteins comprising FVII and a fusion partner linked thereto, but the resulting proteins had the problem of losing their biological activities, even though the short in-vivo half-life was somewhat improved compared to the unfused protein.
Accordingly, there are needs for providing and securing a FVII fusion protein which has an improved in-vivo half-life while retaining the biological activity of the natural type FVII.